This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-4995, filed Jan. 13, 2000; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a backlash correction device and a backlash correction method for preventing the backlash of gears by exerting an urging force to a mobile body moving in forward and backward directions, to one direction.
2. Description of the Related Art
Various types of devices for transmitting a moving force from a driving source to a mobile body through a moving force transmission means having gears allow urging means, such as a spring, to act on the mobile body in one movement direction so as to prevent the erroneous movement of the mobile body due to the backlash of the gears. The specific example of this conventional backlash correction device will be described with reference to FIGS. 1 to 4.
FIG. 1 is a plane view of a paper feed device of a printer or the like to which a backlash correction device is applied. An elevator 1 is vertically, movably provided at a main body base (not shown) and vertically moved by the driving force of an elevator M1. A paper feed base 2, which is a mobile body, is laterally, slidably provided at the elevator 1 by being guided by a guide rail 3. The elevator 1 is provided with a lateral movement motor M2 serving as a driving source and driving force transmission means 4 for transmitting the driving force of this lateral movement motor M2 to the paper feed base 2. The driving force transmission means 4 consists of the first gear G1 fixed to the shaft of the lateral movement motor M2, the second gear G2 engaged with the first gear G1, the third gear G3 engaged with the second gear G2, the fourth gear G4 engaged with the third gear G3 and a rack gear G5 engaged with the fourth gear G4 and fixed to the paper feed base 2.
An extension spring 5 serving as urging means, is provided between the paper feed base 2 and the elevator 1. The paper feed base 2 is urged by the spring force of the extension spring 5 to one direction (which is a left direction in FIG. 1) of the forward and backward movement directions of the base 2. In FIG. 1, reference symbol S1 denotes a lateral HP (home position) sensor detecting the home position of the paper feed base 2. The lateral correction position of the paper feed base 2 is adjusted based on the home position detected by the lateral HP (home position) sensor S1. Reference symbol S2 denotes a paper sensor detecting whether or not paper is present on the paper feed base.
Next, the function of the backlash correction device constituted as stated above will be described. Since the positional relationship among the gears G1 to G5 is relatively determined, description will be given while assuming that each motor-side gears is Ga and each paper feed base-side gear is Gb. As shown in, for example, FIG. 2, the gears Ga and Gb are applied with the spring force f1 of the extension spring 5 and always engaged with each other on their one engagement faces 6a and 7a. In this state, if the paper feed base 2 is moved in an opposite direction to the urging direction of the extension spring 5, the lateral movement motor M2 is driven from the state of FIG. 3(A) to the movement direction of the paper feed base 2 by a predetermined movement quantity. Since the driving force is transmitted in a direction resisting the spring force f1 of the extension spring 5 as shown in FIG. 3(B), the lateral movement motor-side gear Ga and the paper feed base-side gear are engaged with each other on their one engagement faces 6a and 7a and a rotation force is thereby transmitted to the paper feed base 2. Therefore, when the paper feed base 2 is stopped, the lateral movement motor-side gear Ga and the paper feed base-side gear Gb are, as shown in FIG. 3(C), engaged with each other on their one engagement faces 6a and 7a and no backlash naturally occurs.
On the other hand, if the paper feed base 2 is moved in the same direction as the urging force of the extension spring 5, the lateral movement motor M2 is driven from the state of FIG. 4(A) by a predetermined movement quantity in the movement direction of the paper feed base 2. Since this driving force is transmitted in a direction which does not resist the spring force of the extension spring 5 as shown in FIG. 4(B), the lateral movement motor-side gear Ga and the paper feed base-side gear Gb are engaged with each other on their other engagement faces 6b and 7b and a rotation force is thereby transmitted to the paper feed base 2. When the paper feed base 2 is stopped, the lateral movement motor-side gear Ga and the paper feed base-side gear Gb are changed to a state in which they are engaged with each other on their one engagement faces 6a and 7a, thereby preventing the occurrence of backlash.
Namely, according to the conventional case, if the paper feed base 2 is moved in the same direction as the urging direction of the extension spring 5, the paper feed base 2 is forced to be moved by the spring force of the extension spring 5 after the movement of the paper feed base 2 is stopped and the engagement state of the gears Ga and Gb is returned to an original state, thereby preventing the occurrence of backlash.
However, the movement load of the paper feed base 2 varies according to the quantity of the loaded paper. Therefore, if the movement load increases, the spring force f1 of the extension spring 5 cannot force the paper feed base 2 to be moved as shown in FIG. 4(C), with the result that backlash occurs.
Here, it is considered that an extension spring 5 having a stronger spring force is used while supposing a maximum load so as to prevent such backlash from occurring. However, if an extension spring 5 having a too strong spring force is used, it is required to change the lateral movement motor M2 to one having a strong driving force accordingly. If so, a heavy load is always exerted on the respective gears G1 to G5 and the strength, durability and the like of the gears G1 to G5 should be disadvantageously taken into account.
It is an object of the present invention to provide a backlash correction device capable of preventing the occurrence of a movement quantity error caused by the backlash of gears without increasing the urging force of urging means.
A backlash correction device according to the present invention is characterized in that a moving force from a driving source is transmitted to a mobile body through moving force transmission means having at least a gear and the mobile body is urged to one of forward and backward movement directions of the mobile body by the urging force of urging means, thereby preventing the occurrence of a movement quantity error caused by the backlash of the gear, and characterized in that (1) if the mobile body is moved in an opposite direction to an urging direction of the urging means, the driving source is controlled to be driven in a movement direction of the mobile body by a predetermined movement quantity; and (2) if the mobile body is moved in a same direction as the urging direction of the urging means, (2-1) the driving source is controlled to be driven in a movement direction of the mobile body by a movement quantity which is the sum of the predetermined movement quantity and a correction quantity equal to or greater than a maximum backlash quantity and (2-2) then driven in an opposite direction by the correction quantity.
In this backlash correction device, (1) if the mobile body is moved in an opposite direction to an urging direction of the urging means, the driving source is driven in a movement direction of the mobile body by a predetermined movement quantity. In the transmission of the driving force, the gears are engaged with each other against the urging force of the urging means and no backlash, therefore, occurs. (2) If the mobile body is moved in a same direction as the urging direction of the urging means, (2-1) the driving source is driven in a movement direction of the mobile body by a movement quantity which is the sum of the predetermined movement quantity and a correction quantity equal to or greater than a maximum backlash quantity. In the transmission of the driving force, the gears are engaged with each other in a direction which does not resist the urging force of the urging means, and there is a possibility that the gears are separated from each other, i.e., backlash occurs. However, thereafter, (2-2) the driving source is driven in an opposite direction by the correction quantity. By the movement of the driving source in the opposite direction, the gears return to a state in which they are proximate each other on predetermined engagement faces and no backlash, therefore, occurs. Thus, the occurrence of backlash is prevented without increasing the urging force of the urging means.